Infrared sensor

ABSTRACT

A small infrared sensor has a wide infrared light-receiving area (viewing angle), high electromagnetic shielding characteristics, and excellent electromagnetic-wave resistance characteristics. In the infrared sensor, supporting portions are disposed at four corners of a substantially rectangular opening in a package. The supporting portions support an optical filter, disposed so as to cover the opening, at positions that are lower than an upper end of an inner peripheral wall defining the opening. While the optical filter is supported by the supporting portions as a result of inserting a portion of a surface side of the optical filter facing the supporting portions into the opening, the optical filter is secured to the package. The optical filter and the package are joined and secured, and electrically connected to each other through a conductive adhesive.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention of the application relates to an infrared sensor.More particularly, the present invention relates to an infrared sensorhaving a wide viewing angle and detecting infrared radiation, and to aninfrared sensor having improved electromagnetic shieldingcharacteristics.

2. Description of the Related Art

As one type of related infrared sensor used in, for example, human bodydetection and crime-preventing devices, the following infrared sensorwith lead terminals is provided. As shown in FIG. 6, in the infraredsensor, an infrared sensor element 53 having light-receiving electrodes61 disposed on a pyroelectric element 62 is supported on a metallic base(stem) 52 having lead terminals 51. In addition, the infrared sensorelement 53 is accommodated in a cylindrical metallic case (cap) 55including an optical filter 54 provided at the upper surface side of thecase 55 and transmitting infrared radiation. Further, the infraredsensor ordinarily includes a supporting table 63, a substrate 64, abypass capacitor 65, an FET 66, and a resistor 67. The supporting table63 supports the infrared sensor element 53. The substrate 64 has thesupporting table 63 placed thereon, and has necessary electrodes andcircuits (not shown) provided on its surface. The input/output leadterminals 51 (51 a and 51 b) of the infrared sensor pass through themetallic stem 52 through an insulating material 60, and are connected tothe circuits on the substrate 64. The ground lead terminal 51 (51 c) iselectrically connected to the stem 52.

As a mounting structure (mounting method) for mounting the opticalfilter to the metallic case (cap) in such type of infrared sensor, thefollowing mounting structure (mounting method) is proposed. For example,as shown in FIG. 7, the mounting structure (mounting method) is suchthat the optical filter 54 is disposed at an opening window 58 of themetallic case 55 so that the outer surface of the optical filter 54 andthe outer surface of the metallic case 55 are flush with each other. Inaddition, edges of the optical filter 54 and edges defining the openingwindow 58 are adhered and secured to each other with a conductiveadhesive 57. See, for example, Japanese Unexamined Patent ApplicationPublication No. 9-79902.

However, in the infrared sensor in the aforementioned JapaneseUnexamined Patent Application Publication No. 9-79902, the opticalfilter 54 is fitted to a portion (opening window) 58 of the top surfaceof the metallic case 55. Therefore, the entire top surface of themetallic case 55 does not become a light-receiving surface. As a result,an infrared light-receiving area (viewing angle) becomes narrow.

As another type of infrared sensor, the following infrared sensor isproposed. As shown in FIG. 8, in the infrared sensor, an optical filter71 is held by shelves 73, formed at a conductive inner-peripheralheat-transmitting covering member 75, disposed at an inner peripheralportion of a conductive protecting member (package) 72. In addition,using a conductive adhesive 74, end surfaces of the optical filter 71are joined to an inner peripheral surface of the conductiveinner-peripheral heat-transmitting covering member 75, and the bottomsurface of the optical filter 71 is joined to the bottom surfaces of theshelves 73, formed at the conductive inner-peripheral heat-transmittingcovering member 75. As a result, the optical filter 71 is electricallyconnected to the conductive protecting member (package) 72, so thatelectromagnetic shielding characteristics are enhanced. See, forexample, Japanese Unexamined Patent Application Publication No. 8-15007.

However, the structure of the infrared sensor discussed in JapaneseUnexamined Patent Application Publication No. 8-15007 is provided toincrease electromagnetic shielding characteristics and to reduce theinfluence of an ambient temperature change on an infrared sensorelement. As illustrated in FIG. 9 (illustrating an embodiment disclosedin Japanese Unexamined Patent Application Publication No. 8-15007), whenthe infrared sensor has a structure in which portions of a metallicplate 81, which becomes the conductive inner-peripheralheat-transmitting covering member 75, are bent to form the shelves 73 atsubstantially central portions of the respective sides, the shelves 73restrict the viewing angle of the optical filter 71 (see FIG. 8).Therefore, the infrared sensor cannot provide a viewing angle withmaximum efficiency.

SUMMARY OF THE INVENTION

In order to solve the problems described above, preferred embodiments ofthe present invention provide a small infrared sensor that can provide awide infrared light-receiving area (viewing angle), and an infraredsensor having high electromagnetic shielding characteristics andexcellent electromagnetic-wave resistance characteristics.

An infrared sensor according to a preferred embodiment of the presentinvention includes an infrared sensor element, a box package, and anoptical filter. The box package accommodates the infrared sensor elementin an interior thereof so as to allow surface mounting, and has onesubstantially rectangular side that is open. The optical filter isformed so as to transmit infrared radiation of a predeterminedwavelength. In addition, the optical filter is disposed so as to coverthe opening, whose shape is substantially rectangular in plan view, ofthe package. Further, the optical filter functions to cause the infraredsensor element to receive the infrared radiation having thepredetermined wavelength, and functions as a cover that seals theopening, at the same time. Supporting portions are disposed at fourcorners of the opening, whose shape is substantially rectangular in planview, of the package. In addition, the supporting portions support theoptical filter, which is disposed so as to cover the opening, atpositions that are lower than an upper end of an inner peripheral walldefining the opening. While the optical filter is supported by thesupporting portions as a result of inserting a portion of a surface sideof the optical filter facing the supporting portions into the opening,the optical filter is secured to the package.

The optical filter and the package preferably are joined and secured,and electrically connected to each other through a conductive adhesive.

The package preferably includes a metallic package body and aninsulating covering material that covers a main portion of the metallicpackage body. The metallic package body is exposed at an area that isconnected to the optical filter through the conductive adhesive, so thatthe conductive adhesive electrically connects the optical filter and thepackage body to each other.

A peripheral area defining the opening of the package is preferablylower than an outer-side area of the peripheral area defining theopening. The peripheral area cooperates with a side end of a portionprotruding from the upper end of the inner peripheral wall defining theopening of the optical filter, so as to form a holding recess that holdsthe conductive adhesive.

The infrared sensor preferably includes an infrared sensor element, abox package, which accommodates the infrared sensor element in theinterior thereof, and an optical filter, which is disposed so as tocover the opening of the package and functioning simultaneously as afilter and a cover that seals the opening. In the infrared sensor,supporting portions are disposed at four corners of the opening, whoseshape is substantially rectangular in plan view, of the package. Inaddition, the supporting portions support the optical filter, which isdisposed so as to cover the opening, at positions that are lower thanthe upper end of the inner peripheral wall defining the opening. Whilethe optical filter is supported by the supporting portions as a resultof inserting a portion of a surface side of the optical filter facingthe supporting portions into the opening, the optical filter is securedto the package. Therefore, a proportion of a portion (area) that blocksa viewing angle to an entire surface area of the optical filter can beconsiderably reduced. Therefore, practically speaking, it is possible tomount the optical filter to the package without narrowing an infraredlight-receiving area (viewing angle).

Since supporting portions are provided at the four corners of theopening whose shape is substantially rectangular in plan view, theoptical filter is reliably held, so that it is possible to provide ahighly reliable infrared sensor.

When the optical filter and the package are joined and secured to eachother through a conductive adhesive, electrical connection andmechanically joining and securing of the optical filter and the packageto each other can be simultaneously and more reliably performed.Therefore, preferred embodiments of the present invention can be mademore effective.

The package preferably includes a metallic package body and aninsulating covering material that covers a main portion of the metallicpackage body. The metallic package body is exposed at an area that isconnected to the optical filter through the conductive adhesive, so thatthe conductive adhesive electrically connects the optical filter and thepackage body to each other. In this case, it is possible to reliablyprovide a highly reliable ceramic electronic component having theoptical filter and the package electrically connected to each otherwhile being insulated from the outside, so as to provide excellentelectromagnetic shielding characteristics and insulation characteristicswith respect to the outside. Therefore, preferred embodiments of thepresent invention can be made even more effective.

A peripheral area defining the opening of the package is formed lowerthan an outer-side area of the peripheral area defining the opening. Theperipheral area cooperates with a side end of a portion protruding fromthe upper end of the inner peripheral wall defining the opening of theoptical filter, so as to form a holding recess that holds the conductiveadhesive. In this case, it is possible to reliably electrically andmechanically connect the optical filter and the package to each otherwith a conductive adhesive held in the holding recess.

Since the conductive adhesive is held in the holding recess by an amountcorresponding to the volume of the holding recess, excess conductiveadhesive flows up to the central area of the optical filter, so that itis possible to reliably prevent the viewing angle from being narrowed.Therefore, it is possible to provide an infrared sensor providingpredetermined characteristics.

Other features, elements, processes, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of preferred embodiments of the presentinvention with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of an infrared sensor accordingto a preferred embodiment of the present invention.

FIG. 2 shows a state in which an infrared sensor element is accommodatedin a package in the infrared sensor according to a preferred embodimentof the present invention.

FIG. 3 is a perspective view showing a state in which an optical filteris mounted to an opening of the package in the infrared sensor accordingto a preferred embodiment of the present invention.

FIG. 4 is an enlarged view of a main portion of cross section takenalong line I-I of the infrared sensor shown in FIG. 3.

FIG. 5 is an enlarged view of a main portion of a cross section takenalong line II-II shown in FIG. 3.

FIG. 6 shows a structure of a related infrared sensor.

FIG. 7 shows a mounting structure of mounting an optical filter to apackage in the related infrared sensor.

FIG. 8 shows a mounting structure of mounting an optical filter to apackage in another related infrared sensor.

FIG. 9 shows a structure of the main portion of the related infraredsensor shown in FIG. 8.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Features of the present invention will be described below in more detailwith reference to preferred embodiments of the invention.

FIG. 1 is an exploded perspective view of an infrared sensor accordingto a preferred embodiment of the present invention. FIG. 2 shows a statein which an infrared sensor element is accommodated. FIG. 3 is aperspective view showing a state in which an optical filter is mountedto an opening of a package. FIG. 4 is an enlarged view of a main portionof cross section taken along line I-I of the infrared sensor shown inFIG. 3. FIG. 5 is an enlarged view of a main portion of a cross sectiontaken along line II-II shown in FIG. 3.

The infrared sensor includes an infrared sensor element 1, a metallicpackage 2, and an optical filter 3. The package 2 has a box shape andhas one side (top side in FIG. 1) open. In addition, the package 2 haselectrodes 11 (and wiring patterns, etc.) provided in its interiorportion. Further, the package 2 accommodates the infrared sensor element1 in an inner portion (sealing space) 32 so as to allow surfacemounting. The optical filter 3 is disposed so as to completely cover anopening 2 a of the package 2. In addition, the optical filter 3functions to cause the infrared sensor element 1 to receive infraredradiation of a predetermined wavelength and functions as a cover thatseals the opening 2 a of the package 2, at the same time.

As the infrared sensor element 1, a dual-type infrared sensor element ispreferably used. In the dual-type sensor element, two electrodes(light-receiving electrodes) 10 a and 10 b, disposed on a surface of apyroelectric element la polarized in a thickness direction, areconnected in series and with reversed polarity, so that external noise(such as ambient temperature change) input to the two light-receivingelectrodes 10 a and 10 b at the same time is canceled out.

As the package 2, a box package having a substantially completely opentop and formed by covering a main portion of a metallic package body 21by an insulating covering material 22 is used. The package body 2 isformed of a metal, such as 42Ni, phosphor bronze, brass, white metal, oriron. The shape of the opening 2 a of the package 2 in plan viewpreferably is substantially rectangular.

At an area of the package 2 that is connected to the optical filter 3through a conductive adhesive 7 (see FIGS. 3, 4, and 5), the metallicpackage body 21 is exposed, so that the optical filter 3 and the packagebody 21 are electrically connected to each other by the conductiveadhesive 7.

A peripheral area 2 b defining the opening of the package 2 ispreferably lower than an outer-side area 2 c of the peripheral area 2 bof the opening. The peripheral area 2 b cooperates with a side end 3 bof a portion 3 a protruding from an upper end 9 of the inner peripheralwall defining the opening 2 a of the optical filter 3, so as to form aholding recess 15 that holds the conductive adhesive 7 (see FIG. 4).

Bases 12, which support the infrared sensor element 1, are disposed atthe bottom surface of the package 2, and the infrared sensor element 1is supported on the bases 12.

A field effect transistor 19, for defining the infrared sensor, isdisposed in the package 2. In addition, a bypass capacitor, a resistorhaving a high resistance value, etc., are mounted in the package 2 orare integrally provided with the package 2. In FIGS. 1 and 2, thecomponents other than the field effect transistor 19 are not shown.

In the infrared sensor according to the first preferred embodiment,external connection terminals (external electrodes) 5 that are insulatedby an insulating material (not shown) so as not to be electricallyconductive with the package 2 are provided at predetermined locations ofthe metallic package 2. The infrared sensor element 1, disposed in thepackage 2, is formed so as to be electrically connected to the outsidethrough the electrodes and wiring patterns, similarly disposed in thepackage 2, and the external connection terminals (external electrodes)5.

Supporting portions 20 are disposed at four corners 8 of the opening 2a, whose shape is substantially rectangular in plan view, of the package2. The supporting portions 20 support the optical filter 3, which isdisposed so as to cover the opening 2 a, at positions that are lowerthan the upper end 9 of the inner peripheral wall defining the opening 2a.

The supporting portions 20 are formed of the same material as theinsulting covering material 22 that covers the main portion of themetallic package body 21. However, the supporting portions 20 may beformed of a material that is different from the insulating coveringmaterial 22.

As the optical filter 3, an optical filter formed of single-crystalsilicon having a resistance less than or equal to 1 MΩ/cm andtransmitting infrared radiation of a predetermined wavelength ispreferably used. The optical filter 3 preferably has a substantiallyrectangular shape in plan view substantially in correspondence with theopening 2 a in the top surface of the package 2.

As shown in FIG. 4, which is an enlarged view of the main portion of thecross section along the line I-I of the infrared sensor shown in FIG. 3,and as shown in FIG. 5, which is an enlarged view of the main portion ofthe cross section along the line II-II shown in FIG. 3, in the infraredsensor having the above-described structure, the supporting portions 20,disposed at the four corners 8 of the opening 2 a of the package 2,support the optical filter 3 at the positions that are lower than theupper end 9 of the inner peripheral wall defining the opening 2 a. Inaddition, the conductive adhesive 7, supplied to and held by the holdingrecess 15, firmly connects (the side end 3 b of) the optical filter 3and (the opening peripheral area 2 b and the exposed metallic packagebody 21 of) the package 2. Therefore, it is possible to provide aninfrared sensor in which the optical filter 3 and the package 2 arereliably electrically and mechanically connected and secured to eachother.

That is, in the infrared sensor according to a preferred embodiment ofthe present invention, the supporting portions 20, which support theoptical filter 3, disposed so as to cover the opening 2 a, at thepositions that are lower than the upper end 9 of the inner peripheralwall defining the opening 2 a, are provided at the four corners 8 of theopening 2 a of the package 2 a. In addition, while the optical filter 3is supported by the supporting portions 20 as a result of inserting aportion (lower portion) 3 c of a surface side of the optical filter 3facing the supporting portions 20 into the opening 2 a, the opticalfilter 3 is secured to the package 2 with the conductive adhesive 7.Therefore, a proportion of a portion where the viewing angle is blockedby the supporting portions, to an entire surface area of the opticalfilter 3 can be made very low. Consequently, practically speaking, it ispossible to mount the optical filter 3 to the package 2 withoutnarrowing an infrared light-receiving area (viewing angle).

Since the supporting portions 20 are provided at the four corners 8 ofthe opening 2 a having a substantially rectangular shape in plan view,the optical filter 3 is reliably held, so that a highly reliableinfrared sensor can be provided.

As the package 2, a box package having a structure in which the mainportion of the metallic package body 21 is covered by the insulatingcovering material 22 is used. Therefore, while ensuring insulatingcharacteristics with respect to the outside, the optical filter 3 andthe package 2 are reliably electrically connected to each other.Consequently, it is possible to reliably provide a highly reliableceramic electronic component having excellent electromagnet shieldingcharacteristics and insulating characteristics with respect to theoutside.

In addition, the peripheral area 2 b defining the opening of the package2 is formed lower than the outer-side area 2 c of the peripheral area 2b defining the opening. In addition, the peripheral area 2 b cooperateswith the side end 3 b of the portion 3 a of the optical filter 3protruding from the upper end 9 of the inner peripheral wall definingthe opening 2 a, so that the holding recess 15 holding the conductiveadhesive 7 is formed. Therefore, the conductive adhesive 7 held by theholding recess 15 makes it possible to reliably electrically andmechanically connect the optical filter 3 and the package 2 to eachother.

Further, since the conductive adhesive 7 is held in the holding recess15 by an amount corresponding to the volume of the holding recess 15,excess conductive adhesive 7 flows up to the central area of the opticalfilter 3, so that it is possible to reliably prevent the viewing anglefrom being narrowed. Therefore, it is possible to provide an infraredsensor providing predetermined characteristics.

In the first preferred embodiment, an optical filter formed of alow-resistance material (single-crystal silicon) is preferably used asthe optical filter 3. However, it is possible to use, as the opticalfilter 3, an optical filter in which a surface of a filter substrate,formed of an insulating material, is coated with a metallic coating,such as a germanium (Ge) coating, by evaporation or other methods. Thecoating is formed of a low-resistance material. The optical filter 3 isjoined to the metallic package 2 by a conductive adhesive through thecoating formed of the low-resistance material, so that the opticalfilter 3 and the package 2 are in electrical conduction with each other.

As the material of the filter substrate of the optical filter, inaddition to single-crystal silicon, various other materials, such asquartz, sapphire, barium fluoride, and spinel, that transmit infraredradiation may be used.

In the first preferred embodiment, the infrared sensor element is whatis called a dual-type pyroelectric infrared sensor using a pyroelectricelement. However, in the present invention, the type of infrared sensorelement is not particularly limited. Therefore, the present invention isapplicable to an infrared sensor using various other types of infraredsensor elements, such as a single-type element, a quad-type element, athermopile, or a photodiode.

In the first preferred embodiment, as the package 2, a package having astructure in which the main portion of the metallic package body 21 iscovered with the insulating covering material 22 is preferably used.However, the present invention is applicable to a package having astructure in which the main portion is metallic and only a portion thatneeds to be covered with an insulating material is covered with aninsulating material, and to a package in which the main portion isformed of an insulating material, and a conductive material is providedonly on a portion required for electrical connection.

Since the infrared sensor according to the first preferred embodimentincludes the electrodes (and wiring patterns, etc.) 11 in the package 2,the number of electrodes and wiring patterns to be formed on othermembers is reduced, so that the size of a product and the number ofcomponents can be reduced.

Since the package 2 includes the bases 12 that support the infraredsensor element 1, a separate supporting member is not required.Therefore, the number of components and the size of a product can befurther reduced.

Since the bottom portion of the package 2 functions as a stem of arelated infrared sensor, it is possible to reduce the size of a productalso from this viewpoint.

As regards other points, the present invention is not limited to thefirst preferred embodiment. Accordingly, various applications andmodifications may be made within the scope of the present invention asregards, for example, the specific structure and form of the package, orthe type of adhesive (conductive adhesive) for joining the opticalfilter and the package to each other.

As mentioned above, according to preferred embodiments of the presentinvention, it is possible to provide a small infrared sensor notrequiring a complicated structure or a complicated manufacturingprocess, and providing a wide infrared light-receiving area (viewingangle).

In addition, it is possible to provide an infrared sensor havingexcellent electromagnetic shielding characteristics, in which an opticalfilter and a package can be reliably joined together and an infraredsensor element is accommodated in a sealing space formed by the opticalfilter and the package that are electrically connected to each other.

Therefore, the present invention can be widely used in the field of ageneral-purpose infrared sensor used in, for example, detection of ahuman body or crime-preventing devices.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing the scope andspirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

1. An infrared sensor comprising: an infrared sensor element; a boxpackage accommodating the infrared sensor element in an interior thereofso as to allow surface mounting, the package having one substantiallyrectangular side that defines an opening; and an optical filter arrangedso as to transmit infrared radiation of a predetermined wavelength, theoptical filter being disposed so as to cover the opening, whose shape issubstantially rectangular in plan view, of the package, the opticalfilter arranged to cause the infrared sensor element to receive theinfrared radiation having the predetermined wavelength, and arranged todefine a cover that seals the opening; wherein a supporting portion isdisposed at the opening of the package, the supporting portionssupporting the optical filter which is disposed so as to cover theopening, at positions that are lower than an upper end of an innerperipheral wall defining the opening; and while the optical filter issupported by the supporting portion as a result of inserting a portionof a surface side of the optical filter facing the supporting portioninto the opening, the optical filter is secured to the package; whereina peripheral area defining the opening of the package is lower than anouter-side area of the peripheral area defining the opening, and theperipheral area cooperates with a side end of a portion protruding froman upper end of an inner peripheral wall defining an opening of theoptical filter so as to define a holding recess that holds a conductiveadhesive.
 2. The infrared sensor according to claim 1, wherein thepackage includes a metallic package body and an insulating coveringmaterial that covers a main portion of the metallic package body, andthe metallic package body is exposed at an area that is connected to theoptical filter through the conductive adhesive so that the conductiveadhesive electrically connects the optical filter and the package bodyto each other.